Insertion devices that induce a puncturing motion of an insertion needle using a drive mechanism are used to insert sensors for measuring analyte concentrations, for example glucose concentrations, in vivo in a patient's bodily tissue, such as in subcutaneous fatty tissue. Insertion needles commonly used for this purpose are designed as hollow needles or V-shaped grooves in which a sensor is disposed. The sensor can be designed, for example, as an electrode system for electrochemical measurements, or can comprise a microfluidic catheter for the inflow and outflow of perfusion fluid. After a puncture is made, the insertion needle is withdrawn from the bodily tissue and the sensor remains in the puncture site.
Insertion devices are also used, for example, to apply catheters such as for the infusion of insulin or other active agents.
In the case of simple insertion devices, a drive mechanism converts a driving motion of an actuating element into a linear puncturing motion of the insertion needle. The force required to make a puncture must be applied by the user himself using a driving motion of the actuating element during the insertion procedure. As such, many users are reluctant to use such insertion devices on themselves in order to, for example, insert a sensor into the subcutaneous fatty tissue of the abdomen. In particular, persons who have limited range of motion due to age or illness find it difficult to hold an insertion device against their body at the correct angle and apply the proper amount of force required to make a puncture. The action of applying force makes it difficult to hold the insertion device steady and prevent it from tilting during actuation. If the person's hand shakes during puncturing, or if the insertion device tilts, the insertion needle undergoes transverse motions which are painful; in the extreme case, the insertion attempt fails. In particular, transverse motions that occur during puncturing can result in the inserted sensor being ultimately exposed to mechanical stresses from surrounding bodily tissue, which can apply loads upon the sensor and even bend it. In addition, the bodily tissue is constantly irritated, thereby resulting in a greater incidence of inflammation and rejection responses, all of which negatively affect the sensor measurements.
These disadvantages can be largely eliminated by using more complex insertion devices having spring-driven drive mechanisms. In the case of such insertion devices, the energy required for the puncturing motion is delivered by a drive spring or another energy accumulator. For insertion, a user merely needs to place such an insertion device on a suitable point on the body and trigger a puncture by pressing a release element. The amount of force required therefore is minimal, and so even persons who have limited mobility can easily hold the insertion device steady during the insertion procedure.